1. Field of the Invention
The present invention relates to a process for preparing internal olefins. More particularly, it relates to a process for preparing a stable internal olefin by isomerizing a less stable olefin in the presence of a specific catalyst.
2. Description of the Related Art
Various processes are known for isomerizing an olefin to a more stable internal olefin. However, the conventionally known method have various disadvantages such as decomposition of the olefin, formation of undesired polymers from the olefin, and random products formed from the olefin, which are economically unfavorable.
As a catalyst for such isomerization, a liquid base such as a mixture of an alkali metal hydroxide and an aprotic organic solvent, a mixture of an alkali metal amide and an amine, or a mixture of an organic alkali metal compound and an aliphatic amine are known. However, such liquid base has an insufficient catalytic activity on the isomerization of olefin so that expensive agents must be used in a large amount. In addition, it is complicated to recover the component agents of the catalyst from a reaction mass so that not only is a troublesome recovering step necessary but also a large amount of energy is consumed.
As a solid catalyst for isomerization of an olefin, an alkali metal dispersed on a carrier with a large surface area (e.g., activated carbon, silica gel, alumina and the like) is known (cf. J. Am. Chem. Soc., 82, 387 (1960)). However, this catalyst, which comprises alkali metal finely dispersed on the carrier, has unsatisfactory handleability and is less safe since it ignites and loses its activity upon contact with air. Further, this dispersion type catalyst exhibits unsatisfactory isomerization activity.
The present inventors have proposed a solid base which is prepared from alumina, an alkali metal hydroxide and an alkali metal or from water-containing alumina and an alkali metal. The solid base has more excellent isomerization activity and a higher stability to air than the alkali metal dispersion catalyst (cf. Japanese Patent Publication Nos. 3274/1975 and 21378/1982 and U.S. Pat. Nos. 3,808,152, 3,897,509 and 3,928,485). However, such a solid base is still unsatisfactory since an alkali metal should be used for its preparation and its catalytic activity is not necessarily high enough.
Also known is the use of a base catalyst comprising an alkali metal hydride carried on a carrier with a catalytic aid such as ammonia or hydrazine (cf. Japanese Patent Kokai Publication Nos. 121758/1978 and 134736/1984 and U.S. Pat. No. 4,205,192). Since the alkali metal hydride can act as a catalyst in the presence of the catalytic aid such as ammonia or hydrazine, it has some drawbacks in that a purification apparatus for separating and removing the catalytic aid is required and that the catalytic reaction is troublesome due to the use of the catalytic aid.